1 Multithreaded Programming using Java Threads Prof. Rajkumar Buyya Cloud Computing and Distributed Systems (CLOUDS) Laboratory Dept. of Computer Science and Software Engineering University of Melbourne, Australia or

2 Agenda Introduction Thread Applications Defining Threads Java Threads and States Priorities Accessing Shared Resources Synchronisation Assignment 1: Multi-Threaded Math Server Advanced Issues: Concurrency Models: master/worker, pipeline, peer processing Multithreading Vs multiprocessing

3 A single threaded program class ABC { …. public void main(..) { ….. } begin body end

4 A Multithreaded Program Main Thread Thread A Thread BThread C start Threads may switch or exchange data/results

5 Single and Multithreaded Processes Single-threaded Process Single instruction stream Multiple instruction stream Multiplethreaded Process Threads of Execution Common Address Space threads are light-weight processes within a process

6 Server Threads Server Process Client 1 Process Client 2 Process Multithreaded Server: For Serving Multiple Clients Concurrently Internet

7 Web/Internet Applications: Serving Many Users Simultaneously Internet Server PC client Local Area Network PD A

8 Printing Thread Editing Thread Modern Applications need Threads (ex1): Editing and Printing documents in background.

9 Multithreaded/Parallel File Copy reader() { lock(buff[i]); read(src,buff[i]); unlock(buff[i]); } reader() { lock(buff[i]); read(src,buff[i]); unlock(buff[i]); } writer() { lock(buff[i]); write(src,buff[i]); unlock(buff[i]); } writer() { lock(buff[i]); write(src,buff[i]); unlock(buff[i]); } buff[0] buff[1] Cooperative Parallel Synchronized Threads

10 Code-Granularity Code Item Large grain (task level) Program Medium grain (control level) Function (thread) Fine grain (data level) Loop (Compiler) Very fine grain (multiple issue) With hardware Code-Granularity Code Item Large grain (task level) Program Medium grain (control level) Function (thread) Fine grain (data level) Loop (Compiler) Very fine grain (multiple issue) With hardware Task i-l Task i Task i+1 func1 ( ) {.... } func1 ( ) {.... } func2 ( ) {.... } func2 ( ) {.... } func3 ( ) {.... } func3 ( ) {.... } a ( 0 ) =.. b ( 0 ) =.. a ( 0 ) =.. b ( 0 ) =.. a ( 1 )=.. b ( 1 )=.. a ( 1 )=.. b ( 1 )=.. a ( 2 )=.. b ( 2 )=.. a ( 2 )=.. b ( 2 )= x x Load Sockets/ PVM/MPI Threads Compilers CPU Levels of Parallelism

11 What are Threads? A piece of code that run in concurrent with other threads. Each thread is a statically ordered sequence of instructions. Threads are being extensively used express concurrency on both single and multiprocessors machines. Programming a task having multiple threads of control – Multithreading or Multithreaded Programming.

12 Java Threads Java has built in thread support for Multithreading Synchronization Thread Scheduling Inter-Thread Communication: currentThreadstartsetPriority yieldrungetPriority sleepstopsuspend resume Java Garbage Collector is a low-priority thread.

13 Threading Mechanisms... Create a class that extends the Thread class Create a class that implements the Runnable interface Thread MyThread Runnable MyClass Thread (objects are threads) (objects with run() body) [a][b]

14 1st method: Extending Thread class Create a class by extending Thread class and override run() method: class MyThread extends Thread { public void run() { // thread body of execution } Create a thread: MyThread thr1 = new MyThread(); Start Execution of threads: thr1.start(); Create and Execute: new MyThread().start();

15 An example class MyThread extends Thread { public void run() { System.out.println(" this thread is running... "); } class ThreadEx1 { public static void main(String [] args ) { MyThread t = new MyThread(); t.start(); }

16 2nd method: Threads by implementing Runnable interface Create a class that implements the interface Runnable and override run() method: class MyThread implements Runnable {..... public void run() { // thread body of execution } Creating Object: MyThread myObject = new MyThread(); Creating Thread Object: Thread thr1 = new Thread( myObject ); Start Execution: thr1.start();

17 An example class MyThread implements Runnable { public void run() { System.out.println(" this thread is running... "); } class ThreadEx2 { public static void main(String [] args ) { Thread t = new Thread(new MyThread()); t.start(); }

18 Life Cycle of Thread new ready start() running dead stop() dispatch completion wait() waiting sleeping blocked notify() sleep() Block on I/O I/O completed Time expired/ interrupted suspend() resume()

19 A Program with Three Java Threads Write a program that creates 3 threads

20 Three threads example class A extends Thread { public void run() { for(int i=1;i<=5;i++) { System.out.println("\t From ThreadA: i= "+i); } System.out.println("Exit from A"); } class B extends Thread { public void run() { for(int j=1;j<=5;j++) { System.out.println("\t From ThreadB: j= "+j); } System.out.println("Exit from B"); }

21 class C extends Thread { public void run() { for(int k=1;k<=5;k++) { System.out.println("\t From ThreadC: k= "+k); } System.out.println("Exit from C"); } class ThreadTest { public static void main(String args[]) { new A().start(); new B().start(); new C().start(); }

22 Run 1 threads [1:76] java ThreadTest From ThreadA: i= 1 From ThreadA: i= 2 From ThreadA: i= 3 From ThreadA: i= 4 From ThreadA: i= 5 Exit from A From ThreadC: k= 1 From ThreadC: k= 2 From ThreadC: k= 3 From ThreadC: k= 4 From ThreadC: k= 5 Exit from C From ThreadB: j= 1 From ThreadB: j= 2 From ThreadB: j= 3 From ThreadB: j= 4 From ThreadB: j= 5 Exit from B

23 Run2 threads [1:77] java ThreadTest From ThreadA: i= 1 From ThreadA: i= 2 From ThreadA: i= 3 From ThreadA: i= 4 From ThreadA: i= 5 From ThreadC: k= 1 From ThreadC: k= 2 From ThreadC: k= 3 From ThreadC: k= 4 From ThreadC: k= 5 Exit from C From ThreadB: j= 1 From ThreadB: j= 2 From ThreadB: j= 3 From ThreadB: j= 4 From ThreadB: j= 5 Exit from B Exit from A

24 Process Parallelism int add (int a, int b, int & result) // function stuff int sub(int a, int b, int & result) // function stuff pthread t1, t2; pthread-create(&t1, add, a,b, & r1); pthread-create(&t2, sub, c,d, & r2); pthread-par (2, t1, t2); pthread t1, t2; pthread-create(&t1, add, a,b, & r1); pthread-create(&t2, sub, c,d, & r2); pthread-par (2, t1, t2); MISD and MIMD Processing a b r1 c d r2 a b r1 c d r2 add sub Processor Data IS 1 IS 2 Processor

25 do “ d n/2 d n2/+1 “ d n Sort Data IS Data Parallelism sort( int *array, int count) // pthread-t, thread1, thread2; “ pthread-create(& thread1, sort, array, N/2); pthread-create(& thread2, sort, array, N/2); pthread-par(2, thread1, thread2); pthread-t, thread1, thread2; “ pthread-create(& thread1, sort, array, N/2); pthread-create(& thread2, sort, array, N/2); pthread-par(2, thread1, thread2); SIMD Processing Sort Processor

26 Thread Priority In Java, each thread is assigned priority, which affects the order in which it is scheduled for running. The threads so far had same default priority (NORM_PRIORITY) and they are served using FCFS policy. Java allows users to change priority: ThreadName.setPriority(intNumber) MIN_PRIORITY = 1 NORM_PRIORITY=5 MAX_PRIORITY=10

27 Thread Priority Example class A extends Thread { public void run() { System.out.println("Thread A started"); for(int i=1;i<=4;i++) { System.out.println("\t From ThreadA: i= "+i); } System.out.println("Exit from A"); } class B extends Thread { public void run() { System.out.println("Thread B started"); for(int j=1;j<=4;j++) { System.out.println("\t From ThreadB: j= "+j); } System.out.println("Exit from B"); }

28 Thread Priority Example class C extends Thread { public void run() { System.out.println("Thread C started"); for(int k=1;k<=4;k++) { System.out.println("\t From ThreadC: k= "+k); } System.out.println("Exit from C"); } class ThreadPriority { public static void main(String args[]) { A threadA=new A(); B threadB=new B(); C threadC=new C(); threadC.setPriority(Thread.MAX_PRIORITY); threadB.setPriority(threadA.getPriority()+1); threadA.setPriority(Thread.MIN_PRIORITY); System.out.println("Started Thread A"); threadA.start(); System.out.println("Started Thread B"); threadB.start(); System.out.println("Started Thread C"); threadC.start(); System.out.println("End of main thread"); }

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30 Server Threads Message Passing Facility Server Process Client Process User Mode Kernel Mode Multithreaded Server

31 Assignment 1: Multithreaded MathServer – Demonstrates the use of Sockets and Threads Multithreaded MathServer (sin, cos, sqrt, etc.) A Client Program What is sqrt(10)? A Client Program What is sin(10)? A Client Program in “C++” What is sin(10)? A Client Program in “C” What is sin(10)? “sqrt 4.0” “2.0”

32 A Multithreaded Program MathThreads MathSin MathCosMathTan start MathThreads join

33 References Rajkumar Buyya, Thamarai Selvi, Xingchen Chu, Mastering OOP with Java, McGraw Hill (I) Press, New Delhi, India, Sun Java Tutorial – Concurrency: ntial/concurrency/ ntial/concurrency/